1. Field of the Invention
The present invention relates to a piston ring device in an internal combustion engine in which a piston ring is mounted in a ring groove in a piston to come into sliding close contact with an inner wall of a cylinder bore with a predetermined axial gap.
2. Description of the Related Art
The axial gap between the ring groove and the piston ring assumes an important role for ensuring that the piston ring is in close contact with the inner wall of the cylinder bore without being stuck in the ring groove even upon thermal expansion thereof to achieve a good gas sealing function.
However, it has been found by the present inventors that the axial gap is one factor for increasing the concentration of HC in an exhaust gas during the starting or the low-speed operation of the internal combustion engine in a lower-temperature state. This is due to the following reason:
In a conventional piston ring device, as shown in FIGS. 6A and 6B, a piston ring 13 (a compressing ring) mounted in an upper ring groove 10 in a piston 3 is always movable in a range corresponding to an axial gap g between the ring groove 10 and the piston ring 13. Therefore, during ascending of the piston 3 (see FIG. 6A), the piston ring 13 is pushed against a lower surface of the ring groove 10 by its inertial force and a frictional resistance between the ring 13 and the inner wall of the cylinder bore to generate the axial gap g above the piston ring 13. During descending of the piston 3 (see FIG. 6B), the piston ring 13 is pushed against an upper surface of the ring groove 10 by the inertial force and the frictional resistance to shift the gap g to below the piston ring 13.
When the internal combustion engine is at a lower temperature, unburned fuel f deposited to the inner wall of the cylinder is drawn into the gap g generated above the piston ring 13 during ascending of the piston in an exhaust stroke. When the piston ring 13 ascends relative to the piston 3 with its ascending inertial force overcoming the frictional resistance between the ring 13 and the inner wall of the cylinder immediately before a top dead center where the ascending speed of the piston 3 increased suddenly, the unburned fuel f is forced out of the gap g. The unburned fuel f is discharged into an exhaust port along with an exhaust gas to increase the concentration of HC in the exhaust gas.
The present invention has been achieved with such circumstance in view, and it is an object of the present invention to provide a piston ring device in an internal combustion engine, wherein when the internal combustion engine is at a lower temperature, particularly, during the starting or the low-speed operation of the internal combustion engine in which the moving speed of a piston is lower, an increase in concentration of HC in an exhaust gas due to an axial gap between a ring groove and a piston ring can be inhibited.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a piston ring device in an internal combustion engine in which a piston ring is mounted in a ring groove in a piston to come into sliding close contact with an inner wall of a cylinder bore with a predetermined axial gap, wherein a ring restricting means is mounted in the ring groove for restricting an axial movement of the piston ring in the ring groove in a lower-speed operational range of the piston, such restriction being removed in a higher-speed operational range of the piston.
The ring groove and the piston correspond to an upper ring groove 10 and a first compression ring 13 in embodiments of the present invention which will be described hereinafter.
With the first feature, in the lower-speed operational range of the piston, the axial movement of the piston ring in the ring groove is restricted by the ring restricting means and hence, in a lower-temperature and lower-speed operational range of the internal combustion engine, unburned fuel deposited to the inner surface of the cylinder bore cannot flow into and out of the ring groove with the ascending and descending movements of the piston. Therefore, even during an exhaust stroke, the unburned fuel is not released to the outside and hence, it is possible to prevent an increase in concentration of HC in an exhaust gas.
In the higher-speed operational range of the piston, the restriction provided by the ring restricting means is removed and hence, the piston ring can be moved freely vertically within the ring groove and thus prevented from being stuck in the ring groove, thereby exhibiting its intrinsic gas sealing function.
According to a second aspect and feature of the present invention, in addition to the first feature, the ring restricting means comprises a restricting ring which is inserted in a wedge shape between axially opposed surfaces of the ring groove and the piston ring and which has a tension in a direction of insertion, whereby in the lower-speed operational range of the piston, the axial movement of the piston ring within the ring groove is restricted by the wedging action of the restricting ring, and in the higher-speed operational range of the piston, the wedging action of the restricting ring is removed by a floating force of the piston ring generated with the descending movement of the piston.
With the second feature, the ring restricting means can be formed simply by a single member which is the restricting ring and hence, it is possible to prevent an increase in cost for the piston ring device due to the addition of the ring restricting means to a small level.
According to a third aspect and feature of the present invention, in addition to the second feature, mutually opposed surfaces of the piston ring and the restricting ring have slants formed thereon, respectively, so that the restricting ring performs the wedging action.
With the third feature, the restriction of the axial movement of the piston ring can be achieved properly by the wedging action of the restricting ring.
According to a fourth aspect and feature of the present invention, in addition to the third feature, the restricting ring is formed by forming, on an annular flat plate, a plurality of flat portions adapted to contact with an inner surface of the ring groove, and a plurality of inclined portions each having a slant adapted to contact with the slant of the piston ring so that both of the portions are arranged alternately in a circumferential direction.
With the fourth feature, a lightweight restricting ring having a high rigidity can be provided at a low cost using the annular flat plate as a material.